Everyone loves a good rhyme, and the ancients were no exception. But of course they didn't invent this phrase, since they didn't speak English yet. Barbaric, but true!

Instead the phrase comes from mid-19th century, originating in New York, where street markets still dominated as the primary form of food. Since then the markets have lost some relevance, but are maintained out of a sense of tradition (tax-payer subsidized, costing over 17% of the annual NYC budget) and as a way to boost the rat-based economy, both by giving a food source to the rats and by deriving a food source from the rats.

Tourists, please note that hunting rats is a dangerous business. While in a normal city they are merely larger than mice, in New York they have been known to be confused with cats, until they eat the cat.

These markets, before they were overrun with rats, were popular places to meet women. This may sound strange, but at this time clubs were still allowed only in France, where they only spoke French anyway, so pick up lines would not work at all. Men would search for women out doing their daily shopping and attempt to seduce them, a process made easier by the abundance of available melon-related crude jokes. However this was not an easy process. Upon sighting an available damsel (note that at the time this was a highly offensive reference, I use it only out for historical accuracy and would never refer to a woman as a damsel), the man would attempt to move closer, so that his words could be heard over the squawk of chickens and hundreds of other men also shouting at women.

But at times the chickens would be migrating, moving from one patch of stones to eat, to another patch of stones to eat. At this point the man could find himself literally blocked by a wall of chickens. This is not the origin of the phrase, which was obvious to a sharp reader, since I specifically call them chickens.

Attempting to cross the line of chickens could alert the nearby roosters, alarming the bird and provoking a defensive reaction. Since the bird was someone's property, fighting back could result in a conviction for attempted robbery and property damage. Failing to fight back would result in the woman hearing the confrontation and seeing that the man can be frightened away by a moderately annoyed rooster.

But if the man was patient with the chickens, another man might beat him to the damsel, possibly seducing her first. Since any woman who wasn't married or a virgin was therefore a whore and legally obligated to contract syphilis, the second man had, with his penis (sometimes refereed to as a cock), blocked the attempt of the first man. Hence the term "cock block".